The Market Theater Gum Wall is a brick wall covered in used chewing gum, in an alleyway in downtown Seattle. It is located in Post Alley under Pike Place Market.
The wall is by the box office for the Market Theater, and the tradition began around 1993 when patrons of Unexpected Productions’ Seattle Theatresports stuck gum to the wall and placed coins in the gum blobs. Theater workers scraped the gum away twice, but eventually gave up after market officials deemed the gum wall a tourist attraction around 1999.
On November 3, 2015, it was announced by the Pike Place Market Preservation & Development Authority that for the first time in 20 years the gum wall would be receiving a total scrub down for maintenance and steam cleaning, to prevent further erosion of the bricks on the walls from the sugar in the gum. Work began on November 10 and took 130 hours to complete, with over 2,350 pounds (1,070 kg) of gum removed and disposed of. After the cleaning was finished on November 13, gum began to be re-added to the wall; among the first additions were memorials to the November 2015 Paris attacks. (Via Wikipedia)